Here is an article from Shanghai Expat which states that construction on HSR from Kunming to Bangkok could start soon.

Quote:

China-To-Thailand High Speed Railway To Start Construction Early Next Year

In an effort to facilitate tourism between China and Thailand, transport authorities will start construction on a high-speed railway connecting Kunming with Bangkok early next year. The 873-km long railway will also pass through Laos and attain speeds of up to 250 kilometers per hour. It is slated to be completed in approximately five years.